Thanks for replying. I was under the assumption that when It referenced the use of proxies it was talking about them being used at the scatter object in forest pack with which the edge mode doesn't work (in the same way a slice won't hide a proxy) not the fact that you can't use proxies elsewhere in the scene?
Regarding the old edge workaround, we didn't find that this was a suitable way to fix the grass as you could visible see the density change around the edges and with the amount of projects we had to do this on we didn't find it a suitable solution. in the same way that xreffing all the plants isn't viable for our work flow.
Adjusting the global switches doesn't work for us as previously mentioned becuase of the transparency issue but will give the density idea a go on Monday, although I am concerned that his will leave visible patches with no grass on which would be a shame, not so bad for a still photoshop job, but we do animations which would require full cover upon render.